When reading or writing data with an optical disk data recorder drive, such as DVD+RW, there is the possibility of having an inadvertent track jump due to mechanical or other disturbances. An optical disk such as a digital versatile disk (DVD) or compact disk (CD) is typically formatted with tracks formed from a single spiral groove, with each track being considered a 360 degree turn of the spiral. The tracks provide a framework for writing data onto the disk and reading data therefrom. When reading data, for example, a read head is aligned with a desired track of the disk and the data on that track is sensed as the disk rotates past the head. A track jump can be considered as relative displacement of the read/write head from the desired track. Track jumping occurs as a matter of course during operation of an optical disk, to move the read/write head from one disk location to another. Intentional track jumps under control of the disk drive controller typically involve accurate positioning of the read/write head in relation to the disk surface so that the head aligns with another known track at a known time. An unintentional track jump can occur, for example, when a mechanical disturbance of the disk drive causes the read/write head to lose alignment with the desired track of the disk at an unpredictable time and by an unknown radial displacement. Because the timing and displacement from the desired track is unintentional, the disk drive controller can be unaware that the desired track alignment has been lost and the controller may be unable to determine what displacement has occurred in order to correct or compensate for it.
If data is being written to a disk when an unintentional track jump occurs, this can have the undesired effect of overwriting of data on the disk track to which the read/write head has jumped. Accordingly, it is desirable to provide means by which a track jump can be detected. In particular, it is desirable to be able to detect the occurrence of such a jump in a time sufficiently short that the amount of good data that is unintentionally overwritten is sufficiently small to be recovered by a data error correction scheme.
Protection against inadvertent track jumps can be particularly relevant in portable data storage/retrieval applications, such as a camcorder, where there may be mechanical noise and frequent deliberate track jumps to avail of variable bit rate recording. In a less critical situation, track jump detection is valuable in portable data reading applications. A possible situation (for illustrative purposes) would be a many-hour long compilation of MP3 music titles, recorded on a (8-cm) DVD+RW disc. Accurate track jump detection in that case can reduce the likelihood of interruptions to the music during playback, and could also reduce the amount of data buffering which is employed between the read head and the output. A player could avail of the wobble addressing information to detect and correct inadvertent track jumps, and this may help compensate for the lower data signal available from phase change discs.